1. Field of the Invention
The present invention relates to a multifrequency antenna, and more particularly, to a multifrequency antenna containing a slot-type conductor and a strip-shaped conductor.
2. Description of the Prior Art
Recently, the demand for antennas in mobile wireless applications has increased dramatically. In order to increase the use and versatility of antennas, there is a need for a single antenna operable in two or more separate frequency bands. In addition, antennas need to have a small size in order to meet the size requirements of today""s wireless devices.
U.S. Pat. No. 6,195,048 discloses a multifrequency planar inverted F antenna (PIFA). FIG. 1 is a perspective view of a prior art multifrequency planar inverted F antenna 10 disclosed in U.S. Pat. No. 6,195,048. For transmitting and receiving radio signals, the antenna 10 includes an emission conductor 12. The emission conductor 12 comprises a first emission conductor 17 and a second emission conductor 18 that resonate in respectively different frequency bands. The first emission conductor 17 and the second emission conductor 18 are separated by a cutout part 12b in the emission conductor 12. With this construction, the antenna 10 is capable of receiving radio waves of two different frequency bands: a first frequency band determined by the shape of first emission conductor 17 and a second frequency band determined by the shape of second emission conductor 18.
As shown, the first emission conductor 17 has a resonance length LA and the second emission conductor 18 has a resonance length LB. One end of the emission conductor 12 is connected to a ground conductor 11 through a short-circuit plate 13. Power is supplied to a single feeding point 12a of the emission conductor 12 by a coaxial feeding line 14 from power feeding source 15. The coaxial feeding line 14 is connected through a hole 11a provided in ground conductor 11.
With this construction, the antenna 10 resonates in a first frequency band corresponding to length LA of the first emission conductor 17. LA is approximately equal to lambda1/4, where lambda1 is the wavelength of the first frequency. The antenna 10 also resonates in a second frequency band corresponding to length LB of the second emission conductor 18. LB is approximately equal to lambda2/4, where lambda2 is the wavelength of the second frequency. As a result of using the first emission conductor 17 and the second emission conductor 18, the antenna 10 is capable of receiving radio waves of two frequency bands.
However, the prior art antenna 10 uses the short-circuit plate 13 to connect one end of the emission conductor 12 to the ground conductor 11. The use of the short-circuit plate 13 adds extra height, and therefore extra volume, to the antenna 10.
It is therefore a primary objective of the claimed invention to provide a multifrequency antenna with a slot-type conductor and a strip-shaped conductor to solve the above-mentioned problems.
According to the claimed invention, the antenna comprises a metallic plate having a slot. The slot is used to transmit and receive radio signals of a first frequency band. The antenna further comprises a metallic strip connected to the metallic plate for transmitting and receiving radio signals of a second frequency band.
It is an advantage of the claimed invention that the antenna uses both the slot and the metallic strip in order to provide a multifrequency antenna with a smaller height in order to overcome the prior art shortcomings.
These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.